1. Field of the Invention
The present invention relates to an aluminum oxide-titanium nitride sintered body, a manufacturing method thereof, and magnetic head substrates for hard disk drive (hereinafter, referred to as HDD), ultrasonic motors and dynamic pressure bearings using the same.
2. Description of Related Art
Conventionally, composite ceramics consisting of a combination of aluminum oxide and various metal or non-metal carbides, nitrides or the like has been proposed. For example, materials consisting of a combination of aluminum oxide and titanium carbide, or aluminum oxide and titanium nitride have been used for wear resistant members or slide members due to large hardness, and also used for antistatic members due to conductivity.
Specific applications of the above-mentioned include a magnetic head substrate for HDD. FIG. 5(a) is a perspective view showing a general substrate for a magnetic head and FIG. 5(b) is a perspective view showing a magnetic head. As shown in FIG. 5(a), a magnetic head substrate 50 for HDD consists of a composite ceramics mainly composed of aluminum oxide and titanium carbide or aluminum oxide and titanium nitride. Through film forming processes, a number of magnetic head elements 51 are formed on the surface of the magnetic head substrate 50. Subsequently, through individual cutting in slicing process, a magnetic head shown in FIG. 5(b) is obtained.
Since a magnetic head slider 20 that slides on a recording disk (not shown in the drawings) is formed in the magnetic head 52, the magnetic head substrate 50 needs high resistance to wear. Conductivity is also needed to prevent electrostatic damage to the magnetic head element 51. Furthermore, since the magnetic head slider 20 generally flies about several nm high from a recording disk, it is important to highly precisely process a flying surface 20a through ion milling etc. In FIG. 5(b), 20b represents a groove (rail). However, the rail is not limited to groove-like shape and can be convex.
Another application is the pressure member of an ultrasonic motor or the contact surface of a movable member. An ultrasonic motor is a friction drive motor whose drive source is the vibration of piezoelectric elements. Unlike general magnetic drive motors, an ultrasonic motor is not influenced by magnetism and has a high-resolution positioning capability, small size and large driving force, and therefore it is used in zoom mechanism for cameras and magnetic resonance imaging system for medical use. Since the ultrasonic motor is friction-driven, ceramics excellent in resistance to wear and heat has been used as a material for a pressure member which transfers driving force or a contact surface.
FIG. 6 shows an example of an ultrasonic motor. FIG. 6(a) is a schematic illustration showing one principal surface of a general ultrasonic motor and FIG. 6(b) is a schematic illustration showing the other principal surface. As shown in FIG. 6(a), an ultrasonic motor 60 has four divided electrode films 60b on one principal surface of a piezoelectric ceramic plate 60c with wires connected cater-cornered. As shown in FIG. 6(b), an electrode film 60d is formed throughout the other principal surface, thereby preparing a vibrating body 60e. By applying voltages having different phases to the electrode films 60b and 60d, longitudinal vibration and lateral vibration are generated in the piezoelectric ceramic plate 60c. The combination of these vibrations generates elliptic motion in the pressure member 60a. The elliptic motion in the pressure member 60a is transferred to the contact surface of a movable member so as to move the movable member.
For example, an ultrasonic motor is used for guide apparatus. FIG. 7 is a schematic illustration showing guide apparatus in which the ultrasonic motor shown in FIG. 6 is employed. As shown in FIG. 7, guide apparatus 70 has such a structure that a stage 72 is provided on guide members 71 and that the ultrasonic motor 60 is disposed on the contact surface 72a which is the side surface of the stage 72. The ultrasonic motor 60 transfers driving force from the pressure member 60a to the contact surface 72a, thereby moving the stage 72 from side to side.
Such composite ceramics containing aluminum oxide and titanium nitride as used for the above-mentioned applications has been disclosed, for example, in Patent documents 1 to 4. Some conventional materials for magnetic head substrates have been described in Patent documents 5 and 6. In addition, composite ceramics used for the pressure part of an ultrasonic motor has been described in Patent document 7.
Patent document 1 discloses anti-static ceramics which contains one or more of conductive compounds selected from nitrides and carbides of Ti, Zr, Hf, Nb or Ta in a matrix mainly composed of aluminum oxide, and whose surface resistivity is in the range of 106 to 1010 Ω·cm2. It is disclosed that 4 to 23% by volume of conductive compounds are contained and aluminum oxide substantially constitutes the rest, having a mean grain size of not more than 5 μm. In the field of industrial application, the ceramics is proposed as anti-static ceramics for electronic parts to prevent damages caused by rapid discharge when handling charged electronic parts.
Patent document 2 discloses a magnetic head slider wherein one or more selected from SiC, ZrC, TaC, TiC, NbC or TiN are contained in a composite sintered body of Al2O3-10 mole % MgO, Al2O310 mole % SiO2, MgO-2.5 mole % Nb2O5, Al2O3-5 mole % Nb2O5 and Al2O3-10 mole % TiO2, or any oxide of Nb2O5. It discloses that the magnetic head slider can inhibit the wear of a protection film containing carbon or mainly containing carbon in a magnetic disk. That means, since a protection film containing carbon or mainly containing carbon wears off due to the oxidation of the carbon, it is proposed that the magnetic head slider is formed by using materials whose catalysis is small in accelerating the oxidation of the carbon.
Patent document 3 discloses a substrate for manufacturing a thin-film magnetic head wherein a main component consists of Al2O3, TiO2 or Y2O3, stabilizing ZrO2 and wherein the main component contains 2 to 10% by weight of Er in terms of Er2O3. It also discloses a substrate for manufacturing a thin-film magnetic head, wherein the above main component contains not more than 40% by weight of any one or more selected from SiC, ZrC, NbC, TaC, TiC or TiN. In the substrate for manufacturing a thin-film magnetic head, 2 to 10% by weight of Er2O3 is added to the main component. The reason for this is not clear, but as well as the effect of inhibiting the wear of a protection film containing carbon or mainly containing carbon in Patent document 2, a decrease in chipping during machining process or voids during surface polishing is disclosed.
Patent document 4 discloses conductive ceramics obtained by sintering a composition which consists of a mixture of 5 to 70 parts by weight of Al2O3 ceramics containing Al2O3 only or containing not less than 95% by weight of Al2O3 and as conductive material, 30 to 95 parts by weight of at least one or more selected from ZrB2, ZrC, ZrN, TaB2, TaC, TaN, TiB2, TiC and TiN. It also discloses that the since conductive ceramics have a plus figure in resistance temperature characteristic, it does not cause meltdown by a flush of electric current when applying current and heating and it is suitable for heaters or electric igniters.
Patent document 5 discloses a ceramic sintered body (hereinafter, referred to as AlTiC) wherein a main component consists of 60 to 80% by weight of aluminum oxide and 20 to 40% by weight of titanium carbide and the main component contains zirconium oxide, magnesium oxide, yttrium oxide and calcium oxide. It discloses that the ceramic sintered body has better resistance to chipping during slicing process and that it is a magnetic head substrate having low resistance to cutting during machining process.
Patent document 6 discloses a magnetic head substrate that is composed of a sintered body having not less than 99% by weight of silicon carbide, not more than 0.3% by weight of free carbon content and a relative density of not less than 99%. It also discloses that the magnetic head substrate has a heat conductivity of not less than 100 W/m·K, a Young's modulus of not less than 400 GPa, a mean crystal grain size of not more than 10.0 μm and a volume resistivity of 106 to 109 Ω·cm. It discloses that the magnetic head substrate made of silicon carbide has better heat radiating property while maintaining mechanical strength and milling property equivalent to the magnetic head substrate made of AlTiC disclosed in Patent document 5;
Patent document 7 discloses an ultrasonic motor which comprises a vibrating body and a pressure member to transfer the vibration of the vibrating body to a movable member and wherein the pressure member is composed of a composite material of aluminum oxide and titanium carbide. It discloses that the pressure member composed of this composite material makes it possible to inhibit the wear of the pressure member and stabilize the condition of contact. It further discloses that titanium carbide reacts with oxygen in the atmosphere by frictional heat during sliding and turns into titanium oxide having larger coefficient of friction than aluminum oxide or titanium carbide, making it possible to lessen the slip between the pressure member and the movable member side and to transfer driving force without loss.                [Patent document 1] Japanese Unexamined Patent Publication No. 4-230904        [Patent document 2] Japanese Unexamined Patent Publication No. 5-2730        [Patent document 3] Japanese Unexamined Patent Publication No. 6-28632        [Patent document 4] Japanese Unexamined Patent Publication No. 59-78973        [Patent document 5] Japanese Unexamined Patent Publication No. 1-219059        [Patent document 6] Japanese Unexamined Patent Publication No. 2001-56919        [Patent document 7] Japanese Unexamined Patent Publication No. 2003-18870        